JP2895586B2 - Transformer - Google Patents

Description

The present invention relates to a transformer suitable for use as a power transformer for a cycloconverter.

(Prior Art) A circulating current type cycloconverter using this type of transformer is disclosed, for example, in Japanese Patent Application Laid-Open No. 63-186563. This will be described with reference to FIG. A three-phase AC power supply, 2 is a three-phase transformer comprising a power supply winding (primary winding) 3, a positive group winding 4 and a negative group winding 5 (all of which are secondary windings), and 6 is a thyristor 7 having three phases. A positive group converter with a bridge connection, 8 is a negative group converter with a thyristor 9 connected in a three-phase bridge, and 10 and 11 are circulating current limiting reactors connected between the positive and negative DC output terminals of both converters 6 and 8. Reference numeral 12 denotes a load connected between the neutral points of the reactors 10 and 11. In such a cycloconverter, when a gate signal of a predetermined pattern is applied to the gates of the thyristors 7 and 9 of each converter, the output terminals of the positive group converter 6, the output terminals of the negative group converter 8, and the terminals of the load 12 are connected. In FIG. 7, voltages e _op , e _on, and e _o having waveforms indicated by thick lines in FIG. 7 are obtained. Where e _o is e _op
And the average value of e _on . Incidentally, the thin line the output voltage waveform of the three-phase AC power source 1, a dotted line indicates a fundamental wave component of the voltage e _op, e _on and e _o. In this way, the cycloconverter is used as a frequency conversion circuit that directly converts the power supply frequency to an arbitrary frequency within a lower range by controlling the gate signal applied to the gate of the thyristor.

In such a cycloconverter, as shown in FIG. Positive half-wave current i _op is supplied from the thyristor 7 of positive group converter 6, the negative half-wave current i _on of
Is supplied from the thyristor 9 of the negative group converter 8,
Of these, taking i _op as an example, converter 6 has t2-t
During the period in which the thyristor 7 is forward-biased as shown by period 3, the current is also in the forward direction and performs a forward conversion function, and after the thyristor 7 shifts to the reverse bias state as shown by period t3-t4. Also performs the reverse conversion function during the period in which the current continues to flow in the forward direction. During the period in which one converter 6 performs the forward conversion and reverse conversion functions, the other converter 8 is in a standby state for preventing passage of current. However, although such a standby state is formed every half cycle, since the voltage actually includes harmonics as shown in FIG. 7, the standby state is formed between the converters 6 and 8 via the reactors 10 and 11. A circulating current flows. Only a half-wave current flows through the positive group winding 4 and the negative group winding 5 of the transformer 2, whereas the power winding 3 has the same ampere turns of both the positive and negative group windings 4 and 5. Since the full-wave current flows, if the current capacity of the positive or negative group winding is 1, the current capacity of the power supply winding 3 is approximately Is fine.

(Problems to be Solved by the Invention) A conventional three-phase transformer used as a power supply transformer in such a cycloconverter is, for one phase of a three-phase winding, one positive group winding per one leg. The wire, one negative group winding 5 and one power supply winding interposed between these two windings are provided in a concentric arrangement. Therefore, if the load is three-phase, the number of converters must be increased to six and the number of three-phase transformers must be three. Increasing the number of three-phase transformers to three causes an increase in manufacturing cost and an increase in installation space, and further increases the core volume significantly, which causes a problem of increasing no-load loss, particularly iron loss. Such an increase in the no-load loss goes against the intent of adopting a cycloconverter, which attempts to reduce energy consumption by changing the operation system of the induction motor to a variable speed control system.

Accordingly, an object of the present invention is to provide a power transformer connected to a cycloconverter to supply a three-phase alternating current to a three-phase load from a cycloconverter with a single iron core. An object of the present invention is to provide a transformer that can be reduced in size, reduced in size and weight, and reduced in manufacturing cost and installation space.

[Constitution of the Invention] (Means for Solving the Problems) In a transformer used as a power supply of a three-phase output cycloconverter constituted by a positive group converter and a negative group converter, an iron core having a tripod on which a coil is mounted is provided. , A positive group winding, a negative group winding, and a power supply winding, and each of the three positive group windings, Three negative group windings and three power supply windings connected to the negative group converter of each phase are provided, and the three power supply windings provided on each leg are connected in parallel with each other. The three three-phase windings are formed by connecting the three positive group windings provided on each leg over the three legs to form three three-phase windings. The three windings of the negative group are connected in three phases over three legs each to form three three-phase windings. And it features.

(Operation) This transformer is used as a power transformer for a cycloconverter that supplies three-phase AC power to a three-phase load.
Three positive group and negative group windings are assigned to each cycloconverter to apply a three-phase AC voltage to each of the three cycloconverters, and the power supply winding has a winding circuit impedance between the positive and negative groups. One is assigned to a pair of positive and negative group windings to make them identical, and these windings have the structure of a single transformer magnetically coupled to each other by a single tripod core. Although the transformer having such a structure has the same function as having three three-phase transformers, only one iron core is required, and as a result, the core yoke is provided at two places for each tripod core. However, in the present invention, only two locations are required, and the core volume is reduced accordingly.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 4, the tripod-shaped core 21 constituting the transformer 20 in this embodiment has three legs.
22 to 24 and two yoke portions 25 for magnetically coupling between the legs 22 to 24 at the upper and lower ends thereof. FIG. 2 shows the winding structure of the one leg 22. As shown in FIG. 2, three leg group windings Xpu, Ypu, Zpu are formed on the outer periphery of one leg 22 at the innermost layer. Are arranged in the axial direction, three power supply windings Ua, Ub, Uc are similarly arranged on the outer periphery, and three negative group windings Xnu, Ynu, Znu are arranged on the outermost layer. So that each of the three windings is concentric. The same winding arrangement is applied to the other two legs 23 and 24. FIG. 1 shows the relationship between each leg and the windings arranged in this case. In FIG. 1, Xpv to Zpv and Xpw to Zpw are leg 2 respectively.
Positive group windings provided on 3, 24, Xnv to Znv, Xnw to Znw are negative group windings provided on legs 23, 24, respectively, Va to Vc, Wa to Wc are legs, respectively.
These are power supply windings provided on 23 and 24. FIG. 3 shows a three-phase cycloconverter using the transformer 20 as a power supply. In FIG. 3, reference numeral 26 denotes a stator winding 26X, 26 corresponding to a three-phase load, for example, each of three phases X, Y, Z of a star connection.
A three-phase induction motor consisting of Y and 26Z, with three sets of cycloconverters, one set corresponding to one phase for the stator winding of each phase.
The wires are connected so that an AC voltage is applied from each set of 27X, 27Y, and 27Z. Each group of cycloconverters has the same configuration as the positive group cycloconverter 6 and the negative group cycloconverter 8 shown in FIG. That is, 6X, 6Y, 6Z are electric motors
Stator windings 26X, 2 corresponding to the three phases on the 26 side, that is, the X, Y, and Z phases, respectively.
Positive group converters corresponding to 6Y and 26Z, respectively, and 8X, 8Y and 8Z are negative group converters corresponding to the stator windings 26X, 26Y and 26Z, respectively. The connection relationship between such converters and the windings of the transformer 20 is as follows. First, three power supply windings Ua, Ub, Uc provided on the same leg 22 are connected in parallel and connected to the U-phase of the three-phase U, V, W phases of the three-phase AC power supply 1, and The three power supply windings Va, Vb, and Vc provided in 23 are connected in parallel to the V phase of the three-phase AC power supply 1, and the three power supply windings Wa, Wb, and Wc provided in the legs 24 are provided. Are connected in parallel to the W-phase of the three-phase AC power supply 1, and the three sets of parallel windings are three-phase connected as a whole, for example, in a star connection. On the other hand, the three positive group windings Xpu to Xpw and the three negative group windings Xnu to Xnw corresponding to the U, V, and W phases dispersedly arranged on the three legs 22 to 24 respectively have three-phase connection. For example, the star group connection is connected to the positive group converter 6X and the negative group converter 8X corresponding to the X phase, respectively, and the positive group winding Ypu ~ corresponding to the Y phase is also distributed and arranged on the three legs 22 to 24. Ypw and the negative group windings Ynu to Ynw are star-connected, respectively, connected to the positive-phase converter 6Y and the negative-group converter 8Y corresponding to the Y-phase, and further distributed in the three legs 22 to 24. The corresponding positive group windings Zpu to Zpw and the negative group windings Znu to Znw are star-connected, respectively, and connected to the Z-phase corresponding positive group converter 6Z and negative group converter 8Z.

As a result of such a connection configuration, a three-phase AC voltage is applied to the stator windings 26X, 26Y, and 26Z of the induction motor 26 from the cycloconverter, and the frequency of the three-phase AC voltage constitutes each converter. Variable by the control of the gate signal.

The transformer 20 of this embodiment used in a cycloconverter for applying a three-phase AC voltage to a three-phase load conventionally has three transformers, i.e., independent three-phase loads, as shown in FIG. One core compared to three cores 28
21 is fine. 4 and 5, the volume of the iron core will be compared with that of this embodiment by using the dimensions shown (in this case, the thickness of the iron core is assumed to be 1 for convenience).

The volume V of the conventional iron core (the volume of the three cores) is expressed by the following equation.

V = 3 {W (2A + h) -2wh} = 6WA + 3Wh-6wh On the other hand, the volume V 'of the iron core 21 of this embodiment is expressed by the following equation.

V '= W (2A + 3h) -2wh = 2WA + 3Wh-6wh As is apparent from the difference between V and V', the volume of the iron core 21 of this embodiment is smaller by 4WA by 4WA. That is, in the case of a tripod core, two yoke parts are owned per three pieces, so that three pieces have a total of six pieces. However, in the present invention, only two places are required, and the core volume is reduced accordingly. If the material and the magnetic flux density of the iron core are the same, the no-load loss in the iron core is proportional to the volume of the iron core. In addition, since the no-load loss often occurs in the shaded portion of the yoke portion of the iron core in the drawing, the no-load loss is further reduced in the present embodiment in which the number of the yoke portions is reduced as compared with the related art. In addition, the material cost can be reduced as the core volume is reduced, and the number of man-hours for assembling the core is reduced to about 1/3, so that the manufacturing cost can be greatly reduced and the installation space for the core is also reduced to about 1/3. .

Although the winding arrangement in the above embodiment is a concentric arrangement in which the power supply winding is interposed between the positive group winding and the negative group winding in the radial direction of the leg, the present invention is not limited to this. The wires may be coaxially arranged between the positive group winding and the negative group winding in the axial direction of the leg. In the above embodiment,
The connection between each winding and each converter is such that all windings provided on the same leg correspond to only one of the three phases on the power supply side, but the three legs are mutually magnetic. It is not necessary to be bound by such a connection relationship.

[Effect of the Invention] As described above, the present invention is suitable for use as a power supply transformer connected to a cycloconverter for supplying a three-phase alternating current from a cycloconverter to a three-phase load, and This can be constituted by one iron core. As a result, it is possible to provide a transformer that can reduce no-load loss, can be reduced in size and weight, and can reduce the manufacturing cost and the installation space.

[Brief description of the drawings]

1 to 4 relate to an embodiment of the present invention, in which FIG. 1 shows the overall correspondence of the windings of a transformer and FIG. 2 shows the windings on one leg of the transformer. FIG. 3 is a schematic longitudinal sectional view showing the arrangement of the lines, FIG. 3 is a connection diagram of a cycloconverter,
FIG. 4 is a front view of an iron core, FIG. 5 is a front view of a conventional iron core,
FIG. 6 is a connection diagram of the cycloconverter in the case of a single-phase load, FIG. 7 is a voltage waveform diagram of each part in FIG. 6, and FIG. 8 is a time chart showing voltage and current waveforms. In the figure, 21 is an iron core, 22 to 24 are legs, 26 is an induction motor, 6X to
6Z is positive group converter, 8X ~ 8Z is negative group converter, Xpu ~ Z
pw is a positive group winding, Xnu to Znw are negative group windings, and Ua to Wc are power supply windings.

Claims (1)

(57) [Claims] 1. A transformer used as a power source for a three-phase output cycloconverter comprising a positive group converter and a negative group converter, an iron core having a tripod on which a coil is mounted, a positive group winding, and a negative group winding. And three positive-phase windings, each of which is connected to the three-phase positive-phase converter for each leg of the iron core, and three-phase negative-phase converters. Three negative group windings and three power supply windings to be connected are provided, the three power supply windings provided on each leg are connected in parallel with each other, and then connected in three phases, and each leg is connected to each leg. The three positive group windings provided are each connected in three phases over three legs to form three three-phase windings, and each of the three negative group windings provided on each leg is three in number. A three-phase winding formed by three-phase winding over three legs.